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Step 1 > Micro > Flashcards

Micro Flashcards

1
Q

Protein A

A

binds the Fc region of IgG to prevent opsonization and phagocytosis (S. aureus)

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2
Q

IgA protease

A

cleaves IgA and allows bacterial to adhere to and colonize mucosa (S. pneumo, H flu, Neisseria spp)

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3
Q

M protein

A

helps prevent phagocytosis (Group A strep – strep. pyogenes)

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4
Q

Which bacteria have type 3 secretion systems?

A

Salmonella, Shigella, Yersenia, and Pseudomonas

Needle-like appendage facilitating direct delivery of toxins

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5
Q

Transformation

A

ability to take up naked DNA (from cell lysis) from environment (S.pneumo, H flu, and Neisseria)

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6
Q

Conjugation

A

plasmid exchange via sex pilus

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7
Q

Transposition

A

segment of DNA jumps from one location to another, can transfer genes from plasmid to chromosome and vice versa

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8
Q

Genes for which bacterial toxins are encoded in a lysogenic phage

A

ABCD’S

group A strep
Botulism
Cholera
Diphtheria
Shiga toxin
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9
Q

What induces shock in endotoxin producing bacteria

A

Gram negative bacteria
Lipid A – induces shock by activation of macrophages and granulocytes, complement activation, and tissue factor activation

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10
Q

What allows strep viridans to adhere to platelets?

A

Dextrans

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11
Q

What bacteria is optochin sensitive? Optochin resistance?

A

Optochin sensitive = strep pneumo

Optochin resistant = strep viridans

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12
Q

What bacteria is bile soluble? Bile resistant?

A

Bile soluble = strep pneumo (can’t grow in bile)

Bile resistant = strep viridans and enterococcus

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13
Q

What type of infection is an asplenic patient more susceptible to?

A

Encapsulated organisms (Strep pneumo, H. influenza, N meningitides, E coli, Salmonella, Klebsiella, Group B Strep)

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14
Q

3 most common causes of bacterial meningitis in neonates

A

GBS, E coli, listeria

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15
Q

What bacteria is found in soil but does not form spores? How does it present?

A

Nocardia

o Ring enhancing lesions on head CT, pneumonia with cavitary lesions, indurated skin lesions

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16
Q

JONES criteria for rheumatic fever

A 
J: joint pain (arthritis)
O: carditis
N: subcutaneous nodules
E: erythema marginatum
S: sydenham chorea (non rhythmic movements of the hands, feet, and face)
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17
Q

Rheumatic fever results from…?

Poststreptococcal glomerulonephritis results from…?

A

Rheumatic fever results from strep pharyngitis

Poststreptococcal glomerulonephritis results from strep pharyngitis OR impetigo

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18
Q

Causes of conjunctivitis in newborns?

A

o Early onset = gonorrhea

o After several days = chlamydia

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19
Q

Fitz Hugh Curtis syndrome

A

when PID (from gonorrhea or chlamydia) spreads to the peritoneum and causes adhesions to develop to the liver (violin strings)

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20
Q

What form of Chlamydia is infectious?

A

Elementary bodies (then enters the cell and becomes reticulate bodies and divides)

o Elementary bodies are “Enfectious” and Enter the cells
o Reticulate body Replicates

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21
Q

Hektoin agar

A

differentiate Shigella from Salmonella.

o Salmonella grows black colonies while Shigella grows green colonies

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22
Q

What bacteria is grown on charcoal agar with iron and cysteine added?

A

Legionella

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23
Q

Which bacterial infection is associated with hyponatremia?

A

Legionella

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24
Q

Role of urease in H pylori

A

urease splits urea into ammonia and CO2, reduces the acidity of the environment and allows H. pylori to survive in acidic mucosa

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25
Q

H pylori triple therapy

A

Amoxicillin (use Metronidazole if allergic to penicillin)
Clarithromycin
proton pump inhibitor
• Antibiotics Cure Pylori

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26
Q

Cells involved in toxic shock syndrome

A

Superantigens promote the intereaction of T cells and APCs (macrophages) and causes widespread T cell activation

Release of cytokines and inflammatory mediators –> immune cascade

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27
Q

Infectivity of Shigella vs Salmonella

A

Shigella is acid stable: need only a few organisms to cause infection

Salmonella is acid labile: need a lot of organisms to cause infection

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28
Q

Tetanus toxin: prevents the release of which neurotransmitters

A

tetanus toxin travels to spinal cord and cleaves SNARE protein. This inhibits release of GABA and Glycine (inhibitory neurotransmitters), causing spasms

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29
Q

What causes inc susceptibility to recurrent Neisseria infections?

A

MAC complex (C5-C9) deficiency

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30
Q

What accounts for TB’s virulence?

A

Cord factor responsible for inactivating neutrophils, damaging mitochondria, and inducing release of TNF (
Mycobacteria without cord factor cannot cause disease

Sulfatides: inhibit phagolysosome fusion

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31
Q

What causes the formation of a pseudomembrane in C diff?

A

Exotoxin B (depolymerizes actin)

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32
Q

Botulism in adults vs infants

A

Adults: ingestion of preformed toxin
Infants: ingestion of spores that then form toxin

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33
Q

Diagnosis of syphilis

A

VDRL/RPR (nonspecific) and confirm with specific test (FTA-ABS)
• VDRL can be positive in viral infection, drugs, rheumatic fever, lupus and leprosy

34
Q

Tuberculoid leprosy vs. Lepromatous leprosy:

A

o Tuberculoid = well controlled, TH1 response, contained within macrophages, little bacteria within lesions, positive skin test
o Lepromatous = not well contained, TH2 response, humoral response, many bacteria within lesions, negative skin test

35
Q

Causes of atypical pneumonia

A

Mycoplasma, Chlamydia, and Legionella

36
Q

Why doesn’t mycoplasma appear on gram stain?

A

There is no cell wall, they have cholesterol in their plasma membranes (only bacteria like this)
o They are therefore resistant to B lactam antibiotics that target peptidoglycan cell walls

**They have cholesterol in their plasma membrane (unique)

37
Q

Why are Rickettsia and Chlamydia obligate intracellular organisms?

A

they cannot produce CoA or NAD+ so they must get them from eukaryotes

38
Q

What causes staghorn calculi?

A

proteus mirabilis creates an alkaline environment (via urease activity) that allows for precipitation of struvite

39
Q

Difference between Kaposi sarcoma lesions and Bacillary angiomatosis?

A

Kaposi (viral): lymphocytic infiltrate

Bacillary (bacterial): neutrophilic infiltrate

40
Q

Why is ethanol contraindicated with metronidazole?

A

o Can develop a disulfiram-like reaction (disulfiram is a med used for recovering alcoholics).
o It inhibits acetaldehyde dehydrogenase and causes acetaldehyde accumulation – headache, cramps, nausea, flushing).

41
Q

Why can’t Daptomycin be used to treat pneumonia? What is the mechanism of action of this drug?

A

It is inactivated by surfactant

o Mechanism – cyclic lipopeptide that inserts its lipid tail in the cell membrane of gram positive bacteria and causes cell depolarization and death

42
Q

Mechanism of penicillins and cephalosporins? How does resistance develop?

A

interferes with the peptidoglycan cell wall of bacteria by binding to the penicillin binding proteins (transpeptidases) that form the necessary crosslinks – bactericidal

o Alteration in PBPs can lead to resistance

43
Q

Which cephalosporins have activity against pseudomonas?

A

3rd gen (ceftazadine) a “ceftaz treats pseudomonaz”

4th gen (cefepime)

44
Q

How do beta lactam antibiotics work?

A

Bind to penicillin binding proteins (PBPs) and prevent cross linking of peptidoglycan in the bacterial cell wall – causes cell death

45
Q

Differential for rash seen on palms and soles

A

Coxsackie A virus
Rocky mountain spotted fever (Rickettsia)
Secondary syphilis

46
Q

E coli travelers diarrhea toxins

A

Labile toxin increases cAMP

Stable toxin increases cGMP

47
Q

Chloroquine and Primaquine in malaria tx

A

Chloroquine: eradicates plasmodium from the bloodstream
Primaquine: eradicates plasmodia stores in the liver to prevent relapse (add this when tx P. vivax or P. ovale)

48
Q

Reassortment

A

when viruses with segmented genomes exchange genetic material

o Influenza virus – causes antigenic shift

49
Q

Recombination

A

gene exchange that occurs through the crossing over of two double stranded DNA molecules. The resulting progeny can have recombined genomes with traits not present simultaneously in either parent

50
Q

Killed vaccines

A

Induce humoral response only

RIP-Always
Rabies
Influenza
Polio (IPV)
Hep A
51
Q

Live vaccines

A

Induce cellular and humoral responses

Influenza (nasal)
MMR
Yellow Fever
Rotavirus
VZV
Polio (OPV)
Smallpox
52
Q

What is an important side effect of Isoniazid and how does this happen?

A

Isoniazid neuropathy

Isoniazid is chemically similar to vitamin B6 (pyridoxine) and therefore can compete with it in the synthesis of multiple neurotransmitters (inlcuding GABA)

Important to supplement with vitamin B6 to avoid this complicaiton

53
Q

How does the influenza vaccine work?

A

It induces neutralizing antibodies against the hemagglutinin antigen in selected viral strains and prevents the live virus from entering cells

54
Q

Hydrops fatalis

A

Parvovirus B19

55
Q

How is poxvirus different from other DNA viruses?

A

It replicates in the cytoplasm

56
Q

How is herpesvirus different from other enveloped viruses?

A

It gets its envelope from the nuclear membrane of the host cell

(Other viruses get their membrane from the plasma membrane of the host cell)

57
Q

Oseltamivir

A

a neuraminidase inhibitor that prevents virion release from infected cells

58
Q

Neuroaminidase and Hemaglutinin

A 
NA = promotes release of viral progeny
HA = promotes viral entry into host cells
59
Q

Antigenic shift vs antigenic drift

A
  • Antigenic shift = pandemics due to large changes in genome - -due to reassortment
  • Antigenic drift = epidemics due to small changes in genome – due to point mutations in HA or NA
60
Q

What risk is associated with the Rotavirus (Reovirus) vaccine?

A

Inc risk of intussusception (telescoping of the bowels)

61
Q

What cells does EBV infect? What does it do to them?

A

B cells, via CD21

Stimulates B cells to enter the cell cycle and proliferate continuously (”immortalization”) – these immortalized B cells maintain the ability to secrete immunoglobulins

62
Q

What HIV proteins are used to enter the host cell?

A

gp120 (attachment to host CD4 cell)
gp41 (fusion and entry)

Attach to CD4 and CCR5 (on macrophages) or CXCR4 (on T cells)

63
Q

HIV env gene

A

Gp120: attachment to host CD4+ cell
Gp41: fusion and entry

64
Q

HIV gag gene

A

p41 and p17- capsid and matrix proteins, respectively

65
Q

HIV pol gene

A

reverse transcriptase, protease, integrase

66
Q

How does HIV enter cells?

A

Virus binds to CD4 as well as a coreceptor, either CCR5 on macrophages (early infections) or CXCR4 on T cells (late infection)
• People with a homozygous mutation of CCR5 are immune to HIV

67
Q

What drugs should you not take with antacids like calcium carbonate? Why?

A

Tetracylines or Fluoroquinolones – can lead to chelation of the drug and decreased effectiveness

68
Q

Why do we not have a vaccine against Hepatitis C?

A

HCV lacks 3’-5’ exonuclease activity → causes variation in antigenic structures of HCV envelope proteins

69
Q

Hep B replication

A
  1. Virus (partially dsDNA) enters nucleus and the HepB DNA polymerase finishes the partial dsDNA
  2. Host RNA polymerase transcribes mRNA from viral DNA to make viral proteins
  3. The DNA polymerase then reverse transcribes viral RNA to DNA which is the genome of the progeny virus
70
Q

Why does HepD need HepB?

A

The hep B surface antigen must coat the hepatitis D antigen before it can infect and multiply

71
Q

PPD test vs INF gamma release assay

A

PPD test: type IV delayed hypersensitivity
• Will test positive if exposed to BCG vaccine

IFN Gamma release assay: measures the response of T cells when exposed to antigens uniqu to TB
• Advantage: do not test positive if patient was exposed to BCG vaccine

72
Q

What agents are antisporicidal?

A

Hydrogen peroxide – free radical oxygenation

Iodine and iodophors – halogenation of DNA, RNA, and proteins

73
Q

what does H flu require on medium to grow?

A

Factor V: NAD

Factor X: hemin

74
Q

What drug, other than Metronidazole or Vancomycin, can be used for C diff treatment?

A

In patients with recurrent C diff infection, use Fidaxomicin → inhibits the sigma subunit of RNA pol and leads to impairment of protein synthesis and cell death

oral drug with bacteriocidal activity, minimal systemic absorption, and a narrow spectrum; has less effect on noral colonic flora than metronidazole or vancomycin

75
Q

Causes of secondary bacterial pneumonia after an influenza infection

A

Causes of secondary bacterial pneumonia after influenza infection:

Strep pneumo>Staph aureus> H influenzae

76
Q

What type of patient does aspergillus typically affect?

A

Patients with neutropenia (dec neutrophils)

77
Q

How does Aspergillosis cause hepatocellular carcinoma?

A

Via aflatoxin (p53 mutation)

78
Q

Congenital eye problems due to TORCHS infections

A

o Chorioretinitis: CMV and toxoplasmosis

o Congenital cataracts: rubella

79
Q

Patient presents with abdominal discomfort, greasy stool and weight loss. He also complains of joint pain. Intestinal biopsy shows multiple macrophages loaded with PAS-positive granules in the lamina propria? What is this and how should he be treated?

A

Whipple disease: infection with Tropheryma whipplei (intracellular gram positive)
o Decreased lipid transport across enterocyte – lymphatics become blocked with fat

causes malabsorption, cardiac symptoms, arthralgias, and neurologic symptoms – treat with antibiotics

This bacteria proliferate only within macrophages – Foamy macrophages in intestinal lamina propria that are PAS positive (presence of glycoprotein) and contain the rod shaped bacilli

80
Q

Findings in congenital toxoplasmosis

A

Hydrocephalus, intracranial calcifications, and chorioretinitis = classic triad
o In utero infection

81
Q

Neurocysticercosis

A

ingestion of Taenia solium (pork tapeworm) eggs excreted in feces of human carriers
o Common in Central and South America, Africa and Asia

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